• Home

Home > Medical Reference > Encyclopedia (English)

Toggle: English / Spanish

Hemophilia A

• Overview
• Symptoms
• Treatment
• Prevention

Definition:

Hemophilia A is a hereditary bleeding disorder caused by a lack of the blood clotting factor VIII. 

Causes, incidence, and risk factors:

Hemophilia A results from a deficiency (lack) of clotting factor VIII.

The disorder is caused by an inherited X-linked recessive trait, with the defective gene located on the X chromosome. That means the disorder occurs primarily in males. Females carry two copies of the X chromosome, so if the factor VIII gene on one chromosome doesn't work, the gene on the other chromosome can do the job. Males, however, carry only one X chromosome, so if the factor VIII gene on that chromosome is broken, they will have hemophilia A.

If a woman has a defective factor VIII gene, she is considered a carrier. The gene can be passed down to her children. Half of the male babies born from women who carry the defective gene have the disease. Half of the female babies born from women who have the defective gene are carriers. All female children of men with hemophilia carry the defective gene. 

The severity of symptoms can vary. Severe forms become apparent early on. Bleeding is the main symptom of the disease and sometimes, though not always, occurs if an infant is circumcised. Additional bleeding problems are seen when the infant starts crawling and walking.

Mild cases may go unnoticed until later in life when they occur in response to surgery or trauma. Internal bleeding may happen anywhere, and bleeding into joints is common. Risk factors are a family history of bleeding and being male.

• Review Date: 5/3/2006
• Reviewed By: William Matsui, MD, Assistant Professor of Oncology, Division of Hematologic Malignancies, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, MD. Review provided by VeriMed Healthcare Network.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is the first of its kind, requiring compliance with 53 standards of quality and accountability, verified by independent audit. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial process . A.D.A.M. is also a founding member of Hi-Ethics (www.hiethics.com) and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 1997-2007 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.